1. Field of the Invention
The present invention relates to a sheet processing apparatus and an image forming system having a pressing portion that presses a spine of a booklet to deform.
2. Description of the Related Art
Conventionally, when a sheet bundle including about 20 or more sheets is folded, a booklet is formed having a vicinity of a spine being curved. The folded state of the booklet including the sheet bundle folded as described above is insufficient, so that the booklet is soon opened even after it is folded. Therefore, the appearance is degraded. The booklet described above cannot lie flat, so that it is difficult to stack a great number of booklets. To solve this problem, the apparatus described in U.S. Pat. No. 6,692,208 is proposed.
The apparatus described in U.S. Pat. No. 6,692,208 includes a clamping jaw, a stop plate, and a pressing roller. The clamping jaw holds a booklet while it is folded. The stop plate can regulate the height of a booklet spine projecting from the clamping jaw. The pressing roller presses the booklet spine to deform. The apparatus flattens and squares the booklet spine. The apparatus solves the problem of the above-mentioned degraded appearance. Many booklets can be stably stacked.
In general, according to the conventional apparatus as described above, however, a pressing roller supported by a spring moves along the booklet spine. On the other hand, rigidity of the spine of the folded booklet depends on whether or not an image is formed on the spine, the rigidity of the spine is higher at a position where an image is formed. Therefore the spine of the folded booklet does not ensure uniform rigidity over the entire length. When the pressing roller moves on a rigid spine, the spine is insufficiently squared. When the pressing roller moves on a less rigid spine, the spine is squashed excessively.
Taking the above into consideration, the present invention provides a sheet processing apparatus capable of preventing from variability of an amount of squash to a booklet spine when the squaring is performed irrespectively of rigidity of the spine of a folded booklet.